Arcuate dynamic lordotic guard with movable extensions for creating an implantation space posteriorly in the lumbar spine

ABSTRACT

A lordotic guard and method for guiding a bone removal device to form an implantation space in the human spine and, if desired, for inserting a spinal implant into the implantation space.

This application claims the benefit of U.S. provisional application No.60/272,382, filed Mar. 1, 2001, of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a device for implantation into a discspace between adjacent vertebral bodies in the human spine, and a deviceand method for working on those portions of the vertebral bodiesadjacent that disc space to remove bone material and thereby accessvascular bone, and preferably a device and method for protecting theneurological structures such as nerve roots and dural sac proximate theimplantation site while providing protected access to form animplantation space and then access the implantation space formed betweenthe adjacent vertebral bodies for insertion therein of an implant havingupper and lower surfaces being at least in part arcuate. The device andassociated method are used to position (space apart and align) thevertebral bodies, guide the formation of a surface into or through eachof the vertebral body surfaces that are adjacent the intervertebral discspace, and may further be utilized to guide an interbody spinal implanthaving upper and lower surfaces being at least in part arcuate into theimplantation space.

In one embodiment, the device and associated method are used to make animplantation space to insert an implant of a height having a knowncorrespondence to the height of the space created. In anotherembodiment, the device and associated method are used to make animplantation space of known and specific dimensions (e.g., width; depth;and height) and with certain preferred embodiments, permit passagethrough the device of an implant having a height greater than the heightof the implantation space formed through the device.

BACKGROUND OF THE INVENTION

Human vertebral bodies are comprised of a dense, hard outer shell and arelatively less dense inner mass. The hard outer shell is very denselycompacted cancellous bone, resembling cortical bone at all but highmagnification, and is generally referred to as the cortex. The innermass is a softer cancellous bone. As shown in FIG. 1, the outer shell ofcortex bone (the bony endplate) that is adjacent the disc and the boneimmediately beneath that bone (both are subchondral, that is, beneaththe cartilage layer or cartilaginous endplate that separates the bonefrom the disc), are defined for the specific purposes of thisspecification to comprise the “end plate region” to avoid any confusionthat might otherwise arise from any inconsistency in the use of any ofthese terms. While it is understood that these terms may have othermeanings more ordinary or special, and that those of ordinary skill inthe art might otherwise differ as to the correct meanings of theseterms, it is exactly for the purpose of removing any ambiguity thatthese terms are being so precisely defined specifically for thisspecification.

The spinal disc that resides between adjacent vertebral bodies maintainsthe spacing between those vertebral bodies and, in a healthy spine,allows for relative motion between the vertebrae. At the time ofsurgery, for example in the instance of interbody fusion, that is, wherefusion is intended to occur between adjacent vertebral bodies of apatient's spine, the surgeon typically prepares an opening at the siteof the intended fusion by removing a substantial amount of the nucleusdisc material that exists between the adjacent vertebral bodies to befused. Because the outermost layers of bone of the vertebral end plateare relatively inert to new bone growth, the surgeon will typically workon the end plate to remove at least the outermost cell layers of bone togain access to the blood-rich, vascular bone tissue within the vertebralbody. In this manner, the vertebrae are prepared in a way thatencourages new bone growth consistent with fusion.

Devices for assisting a surgeon in accessing the disc space and adjacentvertebral bodies are known. Drill guides and boxed chisels have beenused to form an implantation space between the adjacent vertebral bodiesfor insertion of a spinal implant therein. Applicant invented a guardand instrument system particularly well suited for use in the lumbarspine and of unequalled advantage for use posteriorly therein throughwhich both the implantation space can be formed and a spinal implant canbe inserted into the implantation space, as disclosed in U.S. Pat. No.5,015,247, filed Jun. 13, 1988, which is hereby incorporated byreference.

Applicant also invented a guard having disc penetrating extension(s),which extensions have utility for stabilizing the guard, stabilizing theadjacent vertebrae relative to each other, urging the vertebrae apart ifdesired, and aligning the vertebrae to each other if desired to form theimplantation space through the guard and insert the spinal implantthrough the guard into the implantation space, as disclosed in U.S. Pat.No. 6,080,155 filed Feb. 27, 1995, incorporated herein by reference. Thedisc penetrating extensions can have either parallel or angled upper andlower surfaces in contact with the adjacent vertebral bodies to placethe adjacent vertebral bodies parallel to one another or at an angle toone another. The disclosed disc penetrating extensions are rigid.

To obtain a particular orientation between the adjacent vertebral bodiesa surgeon selects a guard having a predetermined orientation between theupper and lower surfaces of the disc penetrating extensions. In the caseof disc penetrating extensions that have upper and lower surfacesdiverging from one another as would be useful for posterior lumbarinterbody fusion (PLIF), so as to be higher at the insertion or distalend than at the trailing or proximal end of the extensions, a taperedleading end is used to facilitate insertion of the disc penetratingextensions into the disc space. Such a configuration allows for lordosisof the lumbar segment of a spine to be operated upon from a posteriorapproach. For extensions that have diverging upper and lower surfaces,additional force is required to drive the guard and extensions intoplace. Then, after an implant is inserted, it may be difficult to removea distractor element such as a guard having disc penetrating extensionshaving a maximum height greater then the height of the disc spaceposterior height.

Present methods of forming the implantation space between adjacentvertebral bodies generally include the use of one or more of thefollowing: hand held biting and grasping instruments known as rongeurs;drills and drill guides; rotating burrs driven by a motor; andosteotomes and chisels. Applicant has taught various novel instrumentsto mill out the recipient fusion site across the height of the discspace including various cutting/milling frames and various novel cuttersas disclosed in applicant's U.S. application Ser. No. 08/688,758,incorporated herein by reference.

The surgeon must work upon the adjacent end plates of the adjacentvertebrae to access the vascular, cancellous bone that is best suitedfor participating in the fusion and causing active bone growth, and alsoto attempt to obtain an appropriately shaped surface in the vertebralbodies to receive the implant. Because the end plates of the adjacentvertebrae are not flat, but rather have a complex biological as opposedto geometrical curved shape, it is necessary to conform the vertebrae tothe shape of the implant to be received therebetween.

There is a need for a guard for use in posterior lumbar surgery tocreate an interbody implantation space while providing for spinallordosis and while being easily and safely inserted and as easily andsafely removed.

SUMMARY OF THE INVENTION

In accordance with the purposes of the present invention, as embodiedand broadly described herein, a guard of this invention is provided foruse in spinal surgery across a disc space between two adjacent vertebralbodies of a human spine. The guard includes a body having a leading endand an opposite trailing end. The body has a first portion and a secondportion proximate the leading end that are in pivotal relationship toone another between an open position and a closed position. The firstand second portions each have opposed interior portions that are atleast in part arcuate and define an opening for providing protectedaccess to the disc space and the adjacent vertebral bodies. The opposedinterior portions are adapted to guide a bone removal devicetherethrough that is sized to form an implantation space across the discspace and at least in part into the adjacent vertebral bodies. The guardalso includes at least one disc space penetrating extension extendingfrom the leading end of the body that is adapted for insertion at leastin part into the disc space. The extension has a first portion extendingfrom the first portion of the body that has a contact surface adapted tobear against one of the adjacent endplates of the adjacent vertebralbodies. The extension also has a second portion extending from thesecond portion of the body that has a contact surface adapted to bearagainst the other of the adjacent endplates of the adjacent vertebralbodies. The contact surfaces of the first and second portions of theextension are in pivotal relationship to one another from an insertionposition to a deployed position to move the adjacent vertebral bodiesapart upon movement of the first and second portions of the body fromthe open position to the closed position.

The body of the guard may have a generally rectangular or generallysquare cross section along at least a portion of the length of the body.The leading end of the body may be adapted to conform at least in partto the exterior surfaces of the adjacent vertebral bodies by having theleading end cut back to permit the contact surfaces to have an intimatefit with the vertebral bodies when the guard is in the deployedposition. The body may include at least one window adapted to permit thesurgeon to observe the surgery though the window and/or permit portionsof bone extending though the window to be removed by the bone removaldevice passing through the body of the guard.

The guard may include a second disc penetrating extension diametricallyopposite to a first disc penetrating extension. Each disc penetratingextension may have a tapered leading end and have contact surfaces thatare parallel to each other over a substantial portion of the length ofeach extension when in the insertion position. The first and secondportions of each disc penetrating extension may be adapted to touch oneanother when in the insertion position.

The first and second portions of the body may be hinged to one anotherto rotatably articulate relative to one another about an axis ofrotation that is fixed relative to the mid-longitudinal axis of theguard when moved from the open position to the closed position. The bodymay have an interior surface having a cooperating surface for guiding acorresponding cooperating surface on the bone removal device.

The guard may include an impaction cap adapted to cooperatively engagethe trailing end of the body when the body is in the open position. Theguard may include a lock in the form of a collar adapted tocooperatively engage the body of the guard when the body is in theclosed position to hold the body in the closed position.

The guard may form part of a combined spinal surgery set that includes abone removal device, an implant driver, and a spinal implant, or anycombination thereof. The bone removal device may be a drill, mill, orany other device suitable for the intended purpose. The implant may besized and shaped to at least in part match the space formed in the spineby the bone removal device and may be adapted to be combined or treatedwith a natural or artificial bone growth promoting material orsubstance.

In accordance with the purposes of another embodiment of the presentinvention, as embodied and broadly described herein, a guard of thisinvention is provided for use in spinal surgery across a disc spacebetween two adjacent vertebral bodies of the human spine. The guardincludes a body having an opening for providing protected access to thedisc space and the adjacent vertebral bodies. The opening has opposedinterior portions that are at least in part arcuate and adapted to guidetherethrough a bone removal device sized to form an implantation spaceacross the disc space and at least in part into the adjacent vertebralbodies. The guard also includes at least one disc space penetratingextension extending from the body that is adapted for insertion at leastin part into the disc space. The disc penetrating extension has a firstportion having a contact surface adapted to bear against one of theadjacent endplates of the adjacent vertebral bodies and a second portionhaving a contact surface adapted to bear against the other of theadjacent endplates of the adjacent vertebral bodies. The contactsurfaces of the first and second portions are adapted to rotatablyarticulate relative to one another between an insertion position and adeployed position to move the adjacent vertebral bodies apart.

The body has a leading end and an opposite trailing end. The body mayhave a first portion and a second portion proximate the leading end thatare adapted to rotatably articulate relative to one another between anopen position and a closed position.

In accordance with the purposes of a further embodiment of the presentinvention, as embodied and broadly described herein, a method of thisinvention is provided for inserting a spinal implant having at least inpart arcuate upper and lower portions at least in part within and acrossthe generally restored height of a disc space between two adjacentvertebral bodies of a human spine. The method includes the steps ofpositioning into the disc space between the adjacent vertebral bodies aguard having a body and an extension for insertion at least in part intothe disc space and for bearing against end plates of the adjacentvertebral bodies to restore the spacing of the disc space between theadjacent vertebrae, the guard having a first portion oriented toward oneof the adjacent vertebral bodies and a second portion oriented towardanother of the adjacent vertebral bodies, the first and second portionsbeing rotatably articulating relative to one another such that when thebody moves from an open position to a closed position the extensionmoves from an insertion position to a deployed position to move theadjacent vertebral bodies apart; rotatably articulating the guard tomove the body from the open position to the closed position and theextension from the insertion position to the deployed position to movethe adjacent vertebral bodies apart; and forming, through the guard, anopening across height of the disc space and into at least a portion ofthe endplates of the adjacent vertebral bodies, the opening formed intothe endplates having at least in part arcuate surfaces.

The method may include the further steps of performing the spinalimplant surgery from a position posterior to the transverse processes ofthe vertebrae adjacent the disc space; performing the procedure on bothsides of the spinal midline of the spine; securing the body of the guardin the closed position; and inserting two implants into the spine.

The positioning step may include the further steps of positioning aguard having multiple extensions for insertion into the disc space;placing the body of the guard in the open position; driving theextension into the disc space; and inducing angulation to the adjacentvertebral bodies relative to one another.

The rotatably articulating step may include the further steps oforienting the adjacent vertebral bodies in a predetermined relationshiprelative to each other; and inducing lordosis to the adjacent vertebralbodies.

The forming step may include the further steps of inserting the boneremoval device through the guard to a desired depth; forming theimplantation space with the bone removal device; and forming opposedreceiving surfaces in the end plates of the vertebral bodiescorresponding at least in part in size, shape, and contour to an implantto be implanted. The forming step may include any one of milling,drilling, reaming, and trephining the implantation space.

The method may include the further steps of inserting the implant intothe implantation space through the guard, or inserting the implant intothe implantation space after removing the guard from the disc space. Theinserting step may include the further steps of inserting the implantusing an implant inserter; and removing the implant inserter after usingthe implant inserter to insert the implant into the implantation space.The inserting step may also include inserting a spinal implant that is aspinal fusion implant that has at least in part arcuate upper and lowersurfaces for placement between and in contact with the adjacentvertebral bodies, each of the upper and lower surfaces having at leastone opening adapted to permit for the growth of bone from adjacentvertebral body to adjacent vertebral body through the implant. Theinserting step may include inserting a spinal implant having a hollowbetween the upper and lower surfaces; inserting a spinal implant that isexpandable; and inserting a spinal implant having surface projectionsconfigured to resist expulsion of the implant from the implantationspace. The inserting step may include inserting any one of an inertspacer, an artificial disc, or a bone graft.

The inserting step may further include the steps of compressivelyloading the implant with fusion promoting substances selected from oneof bone, bone derived products, demineralized bone matrix, ossifyingproteins, bone morphogenetic protein, hydroxyapatite, and genes codingfor the production of bone; and retaining the fusion promoting substancewithin the implant after the loading step. The step of retaining thefusion promoting substance may include attaching a cap to the implant.

The inserting step may also include the steps of treating the implantwith a fusion promoting substance; inserting an implant in combinationwith a chemical substance adapted to inhibit scar formation; insertingan implant in combination with an antimicrobial material; inserting animplant including a fusion promoting substance or having a bone ingrowthsurface; inserting an implant being at least in part of one of bone andbone growth promoting material; and inserting an implant in combinationwith at least one of a fusion promoting substance, bone, bone growthpromoting material, bone derived products, demineralized bone matrix,ossifying proteins, bone morphogenetic protein, hydroxyapatite, andgenes coding for the production of bone.

The method may further include the steps of collapsing the extensionsand removing the guard form the disc space.

The accompanying drawings, which are incorporated in and constitute apart of this specification, are by way of example only and notlimitation, and illustrate several embodiments of the invention, whichtogether with the description, serve to explain the principles of theinvention. The scope of the invention is limited only by the scope ofthe claims as from the present teachings other embodiments of thepresent invention shall be apparent to those skilled in the art.

OBJECTS OF THE PRESENT INVENTION

The present invention has a number of embodiments, at least some ofwhich have as an object of at least one embodiment of the presentinvention to provide a device and method for quickly, safely,effectively, and accurately spacing apart and positioning a pair ofadjacent vertebral bodies to receive an implant, which is anythingdesigned to be left in the body for an extended length of time, workingupon the properly positioned vertebral body end plate regions adjacent adisc space so as to, remove bone to produce a receiving surface havingan arcuate configuration corresponding to an implant having upper andlower surfaces being at least in part arcuate to be implanted betweenthe adjacent vertebrae.

It is a further object of at least one embodiment of the presentinvention to provide a device and method that permits the insertion ofdisc penetrating extensions of a guard into the disc space posteriorlyin a first position that facilitates insertion and removal of the discpenetrating extensions into and from the disc space and then permits thedisc penetrating extensions to be moved into a second position thatorients the adjacent vertebral bodies in a preferred lordoticrelationship relative to the device and each other.

It is a further object of the present invention, in at least certainembodiments, to provide a device capable of working upon both of thevertebral body end plate regions adjacent a disc space to produceopposed arcuate receiving surfaces in the adjacent end platescorresponding at least in part in size, shape, and contour to an implantto be implanted with the exception of the height of the implant, whichmay be greater than the distance between the opposed receiving surfacesthat may be distracted or otherwise moved apart by insertion of theimplant, and in so doing to define the shape to the implantation space.

It is a further object of the present invention to provide a device thatworks with linear insertion, i.e., insertion along a single axis, andwithout removing the device during the process of disc space preparationand, if so desired with certain embodiments of the present invention,implant placement.

These and other objectives of the present invention will occur to thoseof ordinary skill in the art based on the description of the preferredembodiments of the present invention described below. However, not allembodiments of the inventive features of the present invention needachieve all the objectives identified above, and the invention in itsbroadest aspects is not limited to the preferred embodiments describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings together with the description, serve toexplain the objects, advantages, and principles of the invention. In thedrawings:

FIG. 1 is a top plan view of a horizontal cross section through a bonyend plate region of a vertebral body;

FIG. 2 is a side view of a preferred embodiment of a guard of thepresent invention with the disc penetrating extensions closed into afirst or insertion position;

FIG. 3 is a bottom view of the guard shown in FIG. 2;

FIG. 4 is a side view of the guard of FIG. 2 with the disc penetratingextensions opened into a second or deployed position;

FIG. 5 is an opposite side view of the guard of FIG. 2 with the discpenetrating extensions opened into a second or deployed position;

FIG. 6 is a cross-sectional view of the guard shown in FIG. 3 takenalong line 6—6 of FIG. 3;

FIG. 7 is side cross-sectional view of a lock collar for use with theguard of FIGS. 4 and 5;

FIG. 8 is a side view of an alternative embodiment of a guard with thedisc penetrating extensions opened into a second or deployed portion;

FIG. 9 is a side cross-sectional view of a lock collar for use with theguard of FIG. 8;

FIG. 10 is a perspective view of an impaction cap for use with the guardof FIG. 2 or FIG. 8;

FIG. 11 is a cross-sectional view of the impaction cap of FIG. 10 takenalong line 11—11 of FIG. 10;

FIG. 12 is a rear perspective view of a lumbar segment of a spine withthe dural sac retracted to the left showing a partial discectomy and theguard with disc penetrating extensions of FIG. 2 approaching the discspace between the adjacent vertebral bodies with the disc penetratingextensions in the first or insertion position;

FIG. 13 is a side view of the guard of FIG. 8 inserted fully within thespine with the disc penetrating extensions parallel to one another inthe first or insertion position with the impaction cap of FIG. 10 and aportion of the guard in cross-section on the distal end of the guard;

FIG. 14 is a side view of the guard of FIG. 8 in the deployed positionwith the disc penetrating extensions shown in the second or expandedposition to induce lordosis to the vertebral bodies and the proximal ortrailing end of the guard shown in partial cross-section with thelocking cap of FIG. 9 assembled to maintain the guard in a closedposition;

FIG. 15 shows a proximal end view of a guard in the deployed positionbetween adjacent vertebral bodies with portions of the end plates of theadjacent vertebral bodies visible through the interior of the guard ofFIG. 8;

FIG. 16 shows a side view of the guard of FIG. 8 in the deployedposition with the disc penetrating extensions in an expanded position toinduce angulation to the adjacent vertebral bodies and the distal end ofthe guard shown in cross-section to show a side view of a drill beinginserted through the guard of FIG. 8;

FIG. 17 is a side view of the guard inserted into the adjacent vertebralbodies with the guard in the inserted position with securing end cap onthe distal end thereof and the disc penetrating extensions in theexpanded position showing the portions of the vertebral end platesremoved by the cutting device;

FIG. 18 is a side view of the guard of FIG. 8 with proximal end inpartial cross-section showing a spinal fusion implant and inserterpassing through the guard to insert an implant into the disc spacebetween the adjacent vertebral bodies; and

FIG. 19 shows a side view of the spinal segment with the implant of FIG.25 inserted in the disc space and the guard with the disc penetratingextensions in a first position to facilitate the removal of the guard.

DETAILED DESCRIPTION OF THE PRESENTLY PREFFERED EMBODIMENT

Reference will now be made in detail to the present preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

FIGS. 2-5 are generally directed to an embodiment of a guard having acircular cross-section or having opposed upper and lower arcuateportions for use in spinal surgery for forming an implantation spacebetween adjacent vertebral bodies of the lumbar spine from a posteriorapproach. As shown in FIG. 2, a guard 100 has a body 102 with a firstportion 104 and a second portion 106. Guard 100 also has discpenetrating extensions 110, 112. In particular, first disc penetratingextension 110 extends from first portion 104 of body 102 and second discpenetrating extension 112 extends from second portion 106 of body 102.

In preferred embodiments, but not requisite, various windows 108 inguard body 102 allow the surgeon to remove portions of a facet, pedicle,or spinous process in the same procedure as the bone removal of thevertebral bodies for creating an insertion space therebetween. It iswithin the scope of the present invention to use a variety of windowshapes in addition to the shape depicted to accommodate projecting bonestructures. Window 108 also may be used in observing the procedure atvarious stages of the operation and if so desired for passinginstruments therethrough. Rather than or in addition to a window 108, asbest shown in FIGS. 2-5 and 8, the guard may have one or moreindentations 109 of the wall of the body 102 to make room for a facet,pedicle, or spinous process. Indentation 109, shown in FIG. 3, allowsguard 100 to clear the pedicle of the lower vertebra. Indentation 109,shown in FIG. 5, avoids interference with the bulge of the spinousprocess. Alternatively, indentation 109 of FIG. 5 could be a window toallow bone to protrude inside of guard 100 to be cut off during thedrilling step of the surgical procedure. As best seen in top view FIG.3, disc-penetrating extensions 110, 112 are preferably at least in partcoextensive with the sides 114 of body 102.

FIG. 2 shows guard 100 with body 102 with disc penetrating extensions110, 112 in a first or closed position, for insertion into the discspace between adjacent lumbar vertebral bodies to be operated upon.Whereas FIGS. 4, 5, and 8 show guard 100 with body 102 closed and discpenetrating extensions 110, 112 in a second or expanded or deployedposition. FIG. 6 shows a cross-sectional view of guard 100 with exteriorsurface 116, interior surface 118, and hinges 120.

FIG. 7 is a side cross-sectional view of a lock collar 122 for use withguard 100 of FIG. 2. Lock collar 122 is used when body 102 of guard 100is in the closed position to lock guard 100 into that position.

FIG. 8 is a side view of an alternative embodiment of guard 100including a threaded end 123 for receipt of lock collar 122 of FIG. 9having matching threads 123′.

A perspective view of an impaction cap 124 for use with guard 100 isshown in FIG. 10. FIG. 11 is a cross-sectional view of impaction cap124. Impaction cap 124 is fit over the proximal or trailing end of guard100 with body 102 in the open position and disc penetrating extensions110, 112 in the closed, first, or insertion position. While it may bepossible to insert the extensions of the guard into the disc space byholding the body of guard 100, impaction cap 124 provides a contactsurface 126 upon which force can be applied, such as with a mallet, todrive disc penetrating extensions 110, 112 of guard 100 into the discspace between adjacent vertebral bodies.

FIGS. 12-19 show the progression of various steps of a preferred methodfor using guard 100 and other associated equipment disclosed herein.

FIG. 12 is a perspective view of a segment of a spine viewed from aposterior aspect with the dural sac retracted to the left showing that apartial discectomy has already been performed. Guard 100 with discpenetrating extensions 110, 112 are shown approaching the disc spacebetween the adjacent vertebral bodies with disc penetrating extensions110, 112 in the first or insertion position. Impaction cap 124 ispositioned on the proximal or trailing end of guard 100 to maintain itin the open position such that the disc penetrating extensions areclosed into the insertion position. In this position, guard 100 is readyto be placed or driven into the disc space between the adjacentvertebral bodies.

In FIG. 13, the extensions of guard 100 are fully inserted into thespine with the disc penetrating extensions parallel to one another inthe first or insertion position. Impaction cap 124 is shown holding theguard in the open position and the disc penetrating extension in thefirst or insertion position. While the disc penetrating extensions ofthe first position are shown with a parallel orientation to one another,it is anticipated that the disc penetrating extensions may also be at anangle to one another in the first or closed position. Guard 100rotationally articulates to permit movement of disc penetratingextensions 110, 112 in response to movement of first portion 104 andsecond portion 106 of body 102 relative to one another. The rotationalarticulation preferably occurs about hinge 120, which is preferablyformed in first and second portions 104,106 of body 102.

In FIG. 14, body 102 of guard 100 is shown in a closed position with thedisc penetrating extensions shown in the second, open or insertedposition to induce lordosis to the vertebral bodies. After closing thebody of guard 100, the proximal or trailing end has lock collar 122placed around it to maintain the body of guard 100 in the closedposition. The axis of rotation through hinge 120 is at the back of theadjacent vertebral bodies.

FIG. 15 shows a proximal end view of guard 100 with the body in theclosed and inserted position between adjacent vertebral bodies withportions of the end plates of the adjacent vertebral bodies visiblethrough the interior of guard 100.

In FIG. 16 the body of guard 100 is in a closed position with discpenetrating extensions 110,112 in the second, expanded or insertedposition to induce angulation to the adjacent vertebral bodies. At thedistal end of guard 100 shown in cross-section is a side view of drill128 being inserted through guard 100. Guard 100 provides protectedaccess to the disc space and the adjacent vertebral bodies for drill 128via the elongated opening in guard 100. In one embodiment shown in FIGS.18 and 19, threaded implant 150 having a body sized to match the spaceformed in the spine by drill 128 is screwed into the adjacent vertebralbodies. Drill 128 may have a reduced diameter cutting portion relativeto the shaft diameter or may be inserted through an inner sleeve thatpasses into guard 100 to guide drill 128 to form an implantation spacesmaller than the passage through guard 100. Thus, the guard opening maybe taller than the height of the cutting portion of drill 128. Such ataller opening also allows the implantation of an implant 150 tallerthan the height of the cutting portion of drill 128. For example, ataller oval implant or one with truncated sides may be linearly insertedinto the implantation space having arcuate cuts into the adjacentvertebral bodies. Implant 150 may be threaded, ratcheted, knurled, orhave any other surface projections to facilitate engaging the adjacentvertebral bodies.

FIG. 17 shows the resected bone after removal of drill 128.

As best shown in FIG. 18, an implant 150, such as a threaded interbodyfusion device, motion preserving device or other insert and an inserter152 may be passed through guard 100 to insert implant 150 into the discspace between the adjacent vertebral bodies which guard may be left inplace throughout the procedure.

Implant 150 may be made of artificial or naturally occurring materialssuitable for implantation in the human spine. Implant 150 may also takea variety of shapes, for example, circular or oval in cross section.Implant 150 can comprise bone including, but not limited to, corticalbone. Implant 150 can also be formed of material other than bone, suchas metal including, but not limited to, titanium and its alloys or ASTMmaterial, surgical grade plastics, plastic composites, ceramics, orother materials suitable for use as an interbody implant. The plasticsmay be bioresorbable. Implant 150 can further be formed of bone growthpromoting materials, including but not limited to, bone morphogeneticproteins, hydroxyapatite, and genes coding for the production of bone.Implant 150 can be treated with a bone growth promoting substance, canbe a source of osteogenesis, or can be at least in part bioabsorbable.Implant 150 also can be formed of a porous material. Further, implant150 may be used in combination with chemical substances and/or compoundsapplied at the trailing end of the implant to inhibit scar formation,and a cap may be of benefit in shielding fusion-promoting substancescontained in the implant from these scar formation inhibiting chemicalsand compounds.

As illustrated in FIG. 19, after implant 150 is inserted into theimplantation space into contact between the adjacent vertebral bodies,body 102 of guard 100 is opened and disc penetrating extensions 110, 112are thus placed in the first, closed position to facilitate the removalof guard 100 from the disc space. If not for the ability of theextensions to be retrieved from their lordotic inserted position, therewould be no easy way to remove the guard.

In summary, a preferred method of the present invention includes:performing from a posterior approach in the lumber spine at least apartial laminectomy sufficient for access to the disc space; performingat least a partial discectomy, which more preferably provides sufficientspace to receive the guard disc penetrating extensions to a depth whichmay be generally similar to the depth of implant 150 to be received;retracting and protecting the dural sac; inserting guard 100 withextensions 110,112 into the disc space; inducing lordosis to theadjacent vertebral bodies; securing body 102 of guard 100 in the closedposition; and inserting drill 128 through guard 100 to a desired depth.The depth of insertion may be monitored by x-ray. At this point debrismay be removed by irrigation suction from within and/or about guard 100.Extensions 110, 112 are then collapsed and guard 100 is then removed.Any additional debris may be removed after removal of guard 100, againby irrigation suction. Implant 150 may be inserted through guard 100prior to its removal from the disc space, or may be inserted after guard100 is removed while retractors are utilized as needed to protect theproximate neural structures.

Guard 100 preferably is used for posterior lumbar interbody implantationprocedures. Guard 100 includes a height, a width, and a distance betweenits front and rear portion. The height of body 102 is preferably between8-25 mm and the opening height is preferably 8-20 mm. Disc penetratingextensions 110, 112 may have any shape or configuration suitable for theintended purpose disclosed herein including extensions with parallel orangled upper and lower surfaces in the closed or open position.Preferably, disc penetrating extensions 110, 112 have a combined heightit when closed of 6-18 mm and a length of 12-32 mm. For posterior lumbarinterbody fusion, drill 128 is preferably 8-20 mm in height. Thesedimensions could be greater or less and still be useful for theirintended purpose while still being within the inventive scope of thepresent invention.

Although various embodiments of the present invention have beendisclosed for purposes of illustration and are for purposes of exampleonly and not limitation, it will be understood by those of ordinaryskill in the art that changes, modifications, and substitutions may beincorporated in these embodiments without departing from the spirit orscope of the present invention.

1. A guard for use in human spinal surgery across a disc space betweentwo adjacent vertebral bodies, comprising: a body having a leading endand an opposite trailing end, said body having a first portion and asecond portion in pivotal relationship to one another proximate saidleading end between an open position and a closed position, said firstand second portions having at least in part opposed interior arcuateportions, respectively, said first and second portions defining anopening for providing a protected pathway to the disc space and theadjacent vertebral bodies, said opposed interior arcuate portions beingadapted to guide therethrough a drill sized to form an implantationspace across the disc space and at least in part into the adjacentvertebral bodies; and at least one disc space penetrating extensionextending from said leading end of said body adapted for insertion atleast in part into the disc space, said extension having a first portionextending from said first portion of said body, said first portion ofsaid extension having a contact surface adapted to bear against one ofthe adjacent endplates of the adjacent vertebral bodies, said extensionhaving a second portion extending from said second portion of said body,said second portion of said extension having a contact surface adaptedto bear against the other of the adjacent endplates of the adjacentvertebral bodies, said contact surfaces of said first and secondportions being in pivotal relationship to one another from an insertionposition to a deployed position to move the adjacent vertebral bodiesapart upon movement of said first and second portions of said body fromthe open position to the closed position, said contact surfaces of saidfirst and second portions being pivotal about an axis that passesthrough at least a portion of the pathway to the disc space and theadjacent vertebral bodies.
 2. The guard of claim 1, wherein the axisabout which said contact surfaces pivot intersects the mid-longitudinalaxis of said guard.
 3. The guard of claim 1, wherein the axis aboutwhich said contact surfaces pivot is substantially perpendicular to thesaggital axis of the spine when said guard is engaged to the spine. 4.The guard of claim 1, wherein said extension has a height between saidcontact surfaces, said contact surfaces of said first and secondportions being opposite one another along the height of said extension.5. The guard of claim 1, wherein said opposed interior arcuate portionsof said first and second portions of said body are parallel to oneanother when said body is in the closed position.
 6. The guard of claim1, wherein said opposed interior arcuate portions of said first andsecond portions of said body are angled to one another when said body isin the open position.
 7. The guard of claim 1, wherein said openingdefined by said first and second portions of said body is generallycircular when said body is in the closed position.
 8. The guard of claim1, wherein said opening defined by said first and second portions ofsaid body is generally oval.
 9. The guard of claim 1, wherein saidopening defined by said first and second portions of said body isgenerally elliptical.
 10. The guard of claim 1, wherein said body has anexterior surface that has opposed upper and lower surfaces orientedtoward the adjacent vertebral bodies, respectively, said upper and lowersurfaces being at least in part arcuate.
 11. The guard of claim 10,wherein at least a portion of said upper and lower surfaces of saidexterior surface are parallel to one another when said body is in theclosed position.
 12. The guard of claim 10, wherein at least a portionof said upper and lower surfaces of said exterior surface are angled toone another when said body is in the open position.
 13. The guard ofclaim 10, wherein said exterior surface of said body has opposed sidesurfaces, said side surfaces being at least in part arcuate.
 14. Theguard of claim 13, wherein said side surfaces of said exterior surfaceare parallel to one another.
 15. The guard of claim 1, wherein said bodyhas an exterior surface that has a generally circular cross sectionalong at least a portion of the length of said body.
 16. The guard ofclaim 1, wherein said body has an exterior surface that has a generallyoval cross section along at least a portion of the length of said body.17. The guard of claim 1, wherein said body has an exterior surface thathas a generally elliptical cross section along at least a portion of thelength of said body.
 18. The guard of claim 1, wherein said body has agenerally circular cross section along at least a portion of the lengthof the guard.
 19. The guard of claim 1, wherein said body has agenerally oval cross section along at least a portion of the length ofthe guard.
 20. The guard of claim 1, wherein said body has a generallyelliptical cross section along at least a portion of the length of theguard.
 21. The guard of claim 1, wherein said first and second portionsof said body cooperatively engage along the length of the body when inthe closed position.
 22. The guard of claim 1, wherein said first andsecond portions of said body when in the closed position form a tube.23. The guard of claim 1, wherein said leading end of said body isadapted to conform at least in part to the exterior surface of theadjacent vertebral bodies.
 24. The guard of claim 1, wherein saidleading end of said body is cutback to permit the curvature of the twoadjacent vertebral bodies to have an intimate fit between said body andthe two adjacent vertebral bodies when said contact surfaces are in thedeployed position.
 25. The guard of claim 1, wherein said first andsecond portions of said extension touch one another when in theinsertion position.
 26. The guard of claim 1, wherein said extension hasa height between said contact surfaces and a length sufficient toproperly align and distance apart the adjacent vertebral bodies when inthe deployed position.
 27. The guard of claim 26, wherein said contactsurfaces have a length greater than one half the depth of the disc spacemeasured from the anterior to posterior aspect of the adjacent vertebralbodies.
 28. The guard of claim 1, wherein said contact surfaces areparallel to each other along a substantial portion of the length thereofwhen in the insertion position.
 29. The guard of claim 1, wherein saidbody has an external surface at its leading end and said extension hasan external surface that is at least in part coextensive with saidexternal surface of said body.
 30. The guard of claim 1, wherein saidextension has a tapered leading end to facilitate placement of saidextension into the disc space when in the insertion position.
 31. Theguard of claim 1, further comprising at least a second disc spacepenetrating extension extending from said leading end of said body. 32.The guard of claim 31, wherein said extensions are diametrically opposedto each other and spaced apart from one another to provide access to theadjacent vertebral bodies from within the disc space.
 33. The guard ofclaim 32, wherein said extensions have the same height.
 34. The guard ofclaim 32, wherein said extensions have the same height at the samedistance along their length from said body.
 35. The guard of claim 1,wherein said opposed contacting surfaces diverge away from said bodyalong at least a portion of their length.
 36. The guard of claim 1,wherein said body has at least one window adapted to permit portions ofbone extending through said window to be removed by a drill passingthrough said body.
 37. The guard of claim 1, wherein said body has atleast one window adapted to permit the surgeon to observe surgerythrough said window.
 38. The guard of claim 1, wherein said first andsecond portions of said body are hinged to one another to rotatablyarticulate relative to one another.
 39. The guard of claim 1, whereinsaid first and second portions of said body rotatably articulaterelative to one another about an axis of rotation that is fixed relativeto the mid-longitudinal axis of said guard when moved from the insertionposition to the deployed position.
 40. The guard of claim 1, furthercomprising an impaction cap adapted to cooperatively engage saidtrailing end of said body when said body is in the open position. 41.The guard of claim 1, further comprising a lock adapted to cooperativelyengage said body of said guard when said body is in the closed positionto hold said body in the closed position.
 42. The guard of claim 41,wherein said lock is a collar adapted to cooperatively engage said bodyof said guard when said body is in the closed position to hold said bodyin the closed position.
 43. The guard of claim 42, wherein said collarthreadably engages said trailing end of said body of said guard.
 44. Theguard of claim 1, wherein said body has a height in the range of 8-25mm.
 45. The guard of claim 1, wherein said opening defined by said firstand second portions of said body has a height in the range of 8-20 mm.46. The guard of claim 1, wherein said extension has a combined heightwhen closed in the range of 6-18 mm.
 47. The guard of claim 1, whereinsaid extension has a length in the range of 12-32 mm.
 48. The guard ofclaim 1, in combination with a bone removal device for forming throughsaid guard an implantation space across the disc space.
 49. The guard ofclaim 48, wherein said bone removal device is selected from the groupconsisting of a drill, a trephine, a reamer, an end mill, a chisel, anda burr.
 50. The guard of claim 48, wherein said bone removal device hasa height in the range of 8-20 mm.
 51. The guard of claim 1, incombination with an implant driver sized in part for passage throughsaid opening for passing an implant through said guard and into the discspace.
 52. The guard of claim 51, wherein said implant driver comprisesa shaft adapted to engage the implant at one end and a handle formanipulating said implant driver at the other end of said shaft.
 53. Theguard of claim 1, in combination with a spinal implant adapted to beinserted in the implantation space formed through said guard.
 54. Theguard of claim 53, wherein said implant comprises at least one of boneand bone growth promoting material.
 55. The guard of claim 54, whereinsaid bone growth promoting material is selected from one of bone, bonederived products, demineralized bone matrix, ossifying proteins, bonemorphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 56. The guard of claim 53, wherein said implant isin combination with a bone growth promoting material.
 57. The guard ofclaim 56, wherein said bone growth promoting material is selected fromone of bone, bone derived products, demineralized bone matrix, ossifyingproteins, bone morphogenetic protein, hydroxyapatite, and genes codingfor the production of bone.
 58. The guard of claim 53, wherein saidimplant is treated with a bone growth promoting substance.
 59. The guardof claim 53, wherein said implant comprises at least one of thefollowing materials: metal, titanium, plastic, and ceramic appropriatefor implantation in the human body.
 60. The guard of claim 53, whereinsaid implant is at least in part resorbable.
 61. The guard of claim 53,wherein said implant is formed of a porous material.
 62. The guard ofclaim 53, in combination with a chemical substance adapted to inhibitscar formation.
 63. The guard of claim 53, in combination with anantimicrobial material.
 64. The guard of claim 1, in combination with animplant sized and shaped to at least in part match the space formed inthe spine by a bone removal device.
 65. A guard for use in human spinalsurgery across a disc space between two adjacent vertebral bodies,comprising: a body having an opening for providing a protected pathwayto the disc space and the adjacent vertebral bodies, said opening havingat least in part opposed interior arcuate portions adapted to guidetherethrough a drill sized to form an implantation space across the discspace and at least in part into the adjacent vertebral bodies; and atleast one disc space penetrating extension extending from said bodyadapted for insertion at least in part into the disc space, said discpenetrating extension having a first portion having a contact surfaceadapted to bear against one of the adjacent endplates of the adjacentvertebral bodies and a second portion having a contact surface adaptedto bear against the other of the adjacent endplates of the adjacentvertebral bodies, said contact surfaces of said first and secondportions being rotatably articulating relative to one another between aninsertion position and a deployed position to move the adjacentvertebral bodies apart, said contact surfaces of said first and secondportions being pivotal about an axis that passes through at least aportion of the pathway to the disc space and the adjacent vertebralbodies.
 66. The guard of claim 65, wherein said opposed interiorportions of said body are parallel to one another.
 67. The guard ofclaim 65, wherein said opposed interior portions of said body are angledto one another.
 68. The guard of claim 65, wherein said opening isgenerally circular.
 69. The guard of claim 65, wherein said opening isgenerally oval.
 70. The guard of claim 65, wherein said opening isgenerally elliptical.
 71. The guard of claim 65, wherein said body hasan exterior surface that has opposed upper and lower surfaces orientedtoward the adjacent vertebral bodies, respectively, said upper and lowersurfaces being at least in part arcuate.
 72. The guard of claim 71,wherein said body has an exterior surface that has opposed sidesurfaces, said side surfaces being at least in part arcuate.
 73. Theguard of claim 72, wherein said side surfaces of said exterior surfaceare parallel to one another.
 74. The guard of claim 65, wherein saidbody has an exterior surface that has a generally circular cross sectionalong at least a portion of the length of said body.
 75. The guard ofclaim 65, wherein said body has an exterior surface that has a generallyoval cross section along at least a portion of the length of said body.76. The guard of claim 65, wherein said body has an exterior surfacethat has a generally elliptical cross section along at least a portionof the length of said body.
 77. The guard of claim 65, wherein said bodyhas a generally circular cross section along at least a portion of thelength of the guard.
 78. The guard of claim 65, wherein said body has agenerally oval cross section along at least a portion of the length ofthe guard.
 79. The guard of claim 65, wherein said body has a generallyelliptical cross section along at least a portion of the length of theguard.
 80. The guard of claim 65, wherein said body has a leading endadapted to conform at least in part to the exterior surface of theadjacent vertebral bodies.
 81. The guard of claim 65, wherein said bodyhas a leading end that is cutback to permit the curvature of the twoadjacent vertebral bodies to have an intimate fit between said body andthe two adjacent vertebral bodies when said contact surfaces are in thedeployed position.
 82. The guard of claim 65, wherein said first andsecond portions of said extension touch one another when in theinsertion position.
 83. The guard of claim 65, wherein said extensionhas a height between said contact surfaces and a length sufficient toproperly align and distance apart the adjacent vertebral bodies when inthe deployed position.
 84. The guard of claim 83, wherein said contactsurfaces have a length greater than one half the depth of the disc spacemeasured from the anterior to posterior aspect of the adjacent vertebralbodies.
 85. The guard of claim 65, wherein said contact surfaces areparallel to each other along a substantial portion of the length thereofwhen in the insertion position.
 86. The guard of claim 65, wherein saidbody has an external surface and said extension has an external surfacethat is at least in part coextensive with said external surface of saidbody.
 87. The guard of claim 65, wherein said extension has a taperedleading end to facilitate placement of said extension into the discspace when in the insertion position.
 88. The guard of claim 65, furthercomprising at least a second disc space penetrating extension extendingfrom said body.
 89. The guard of claim 88, wherein said extensions arediametrically opposed to each other and spaced apart from one another toprovide access to the adjacent vertebral bodies from within the discspace.
 90. The guard of claim 89, wherein said extensions have the sameheight.
 91. The guard of claim 89, wherein said extensions have the sameheight at the same distance along their length from said body.
 92. Theguard of claim 65, wherein said opposed contacting surfaces diverge awayfrom said body along at least a portion of their length.
 93. The guardof claim 65, wherein said body has at least one window adapted to permitportions of bone extending through said window to be removed by the boneremoval device passing through said body.
 94. The guard of claim 65,wherein said body has at least one window adapted to permit the surgeonto observe the surgery through said window.
 95. The guard of claim 65,wherein said first and second portions of said disc space penetratingextension are hinged to one another to rotatably articulate relative toone another.
 96. The guard of claim 65, wherein said first and secondportions of said disc space penetrating extension rotatably articulaterelative to one another about an axis of rotation that is fixed relativeto the mid-longitudinal axis of said guard when moved from the insertionposition to the deployed position.
 97. The guard of claim 65, furthercomprising an impaction cap adapted to cooperatively engage a trailingend of said body.
 98. The guard of claim 65, wherein said body has aheight in the range of 8-25 mm.
 99. The guard of claim 65, wherein saidopening of said body has a height in the range of 8-20 mm.
 100. Theguard of claim 65, wherein said extension has a combined height whenclosed in the range of 6-18 mm.
 101. The guard of claim 65, wherein saidextension has a length in the range of 12-32 mm.
 102. The guard of claim65, in combination with a bone removal device for forming through saidguard an implantation space across the disc space.
 103. The guard ofclaim 102, wherein said bone removal device is selected from the groupconsisting of a drill, a trephine, a reamer, an end mill, a chisel, anda burr.
 104. The guard of claim 102, wherein said bone removal devicehas a height in the range of 8-20 mm.
 105. The guard of claim 65, incombination with an implant driver sized in part for passage throughsaid opening for passing an implant through said guard and into the discspace.
 106. The guard of claim 105, wherein said implant drivercomprises a shaft adapted to engage the implant at one end and a handlefor manipulating said implant driver at the other end of said shaft.107. The guard of claim 65, in combination with a spinal implant adaptedto be inserted in the implantation space formed through said guard. 108.The guard of claim 65, in combination with an implant sized and shapedto at least in part match the space formed in the spine by a boneremoval device.
 109. The guard of claim 107, wherein said implantcomprises at least one of bone and bone growth promoting material. 110.The guard of claim 109, wherein said bone growth promoting material isselected from one of bone, bone derived products, demineralized bonematrix, ossifying proteins, bone morphogenetic protein, hydroxyapatite,and genes coding for the production of bone.
 111. The guard of claim107, wherein said implant is in combination with a bone growth promotingmaterial.
 112. The guard of claim 111, wherein said bone growthpromoting material is selected from one of bone, bone derived products,demineralized bone matrix, ossifying proteins, bone morphogeneticprotein, hydroxyapatite, and genes coding for the production of bone.113. The guard of claim 111, wherein said implant is treated with a bonegrowth promoting substance.
 114. The guard of claim 111, wherein saidimplant comprises at least one of the following materials: metal,titanium, plastic, and ceramic appropriate for implantation in the humanbody.
 115. The guard of claim 111, wherein said implant is at least inpart resorbable.
 116. The guard of claim 111, wherein said implant isformed of a porous material.
 117. The guard of claim 111, in combinationwith a chemical substance adapted to inhibit scar formation.
 118. Theguard of claim 111, in combination with an antimicrobial material. 119.The guard of claim 65, wherein the axis about which said contactsurfaces pivot intersects the mid-longitudinal axis of said guard. 120.The guard of claim 65, wherein the axis about which said contactsurfaces pivot is substantially perpendicular to the saggital axis ofthe spine when said guard is engaged to the spine.
 121. The guard ofclaim 65, wherein said extension has a height between said contactsurfaces, said contact surfaces of said first and second portions beingopposite one another along the height of said extension.